Method of determining the quality of voice data with transmission via a network, method of and an apparatus for performing a telephone call

ABSTRACT

A method of determining the quality of transmitted voice data can include:providing voice data at a transmitter side in a first data format,providing a first test signal in the first data format,combining the voice data and the test signal to form input data,transmitting the input data in a transmittal data format,receiving the transmitted input data at a receiver side to obtain output data,removing at least portions of a data packet in the output data or of a data packet derived therefrom in order to derive a second test signal, andanalysing the derived second test signal by applying a predetermined analysis criterion in order to obtain at least one value for a quality indicator. An apparatus and system can also be configured to utilize embodiments of the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national stage application ofInternational Patent Application No. PCT/EP2018/079305, filed on Oct.25, 2018 and claiming priority to European Patent Application No.17198963.5, filed on Oct. 27, 2017.

FIELD

The invention relates to a method of determining the quality oftransmitted voice data, in particular of speech data transmitted duringa telephone call, and further relates to a method of and an apparatusfor performing a telephone call.

BACKGROUND

US 2009/238085 A1 discloses a digital signal processor at a receiverside that extracts quality factors for each of packet delay, jitter,packet loss and signal energy information in order to determine adynamic voice quality value for the endpoint, with the purpose to obtainon the basis of these quality factors, from a lookup table, the dynamicvoice quality at the endpoint. The resources of processing time forrespective calculations are high, if a good assessment of quality is tobe achieved.

US 2017/104867 A1 discloses to analyse at an endpoint terminaltransmission information and/or acoustic quality information but remainssilent as to details of such analysis.

US 2003/009306 A1 relates to voice-aided diagnostic for a voice overinternet protocol based device, wherein self diagnostic tasks areinvoked through voice commands. Hence, the voice quality is notpermanently controlled.

U.S. Pat. No. 7,830,860 B2 deals with packet data network voice callmonitoring, wherein regularly, ping request packets are transmitted,namely during silent intervals. The disadvantage thereof lies in thatjust when a good voice quality is not needed, during silence, theanalysis is made.

The company Selvana Oü, Roosikrantsi to 2, Tallinna linn,

Harjumaakond, 10119 Estonia, offers a product called AQuA wherein audioreference signals are inserted into the transmitted data, for qualitycontrol.

U.S. Pat. No. 8,593,975 A as well describes to insert reference testpackets into transmitted actual streaming packets in a packet-basednetwork, these reference test packets for enabling voice qualityanalysis. The document mentions that measures need to be taken for thelistener not to be disturbed by the insertion of the reference testpackets.

SUMMARY

It is the object of the present invention to provide for a method ofdetermining the quality of voice data with transmission via a network,wherein the information is more steadily available, and without toextensively affecting itself the voice data audible to the listener. Theobject further includes providing a method of performing a telephonecall with quality determination, and a respective apparatus.

In some embodiments, the object of the present invention can be solvedby a method of determining the quality of transmitted voice data, amethod of performing a telephone call, apparatuses (transmitter side andreceiver side), and a communication system.

Embodiments of a method of determining the quality of transmitted voicedata, in particular of speech data transmitted during a telephone call,wherein the voice data are transmitted via a network, can include:

-   -   providing voice data at a transmitter side in a first data        format (which might be the original analogue data format, or a        digital data format derived therefrom),    -   providing a first, transmitter side test signal in the (same)        first data format,    -   combining the voice data and the test signal to form input data        (wherein such combining shall include that the data content in        at least one minimum data unit of the voice data is changed on        the basis of at least part of the test signal to a different        data content, namely preferably in the same at least one minimum        data unit, and preferably without changing the at least one        minimum data unit as to its definition and size),    -   transmitting the input data in a transmittal data format,    -   receiving the transmitted input data at a receiver side to        obtain output data,    -   removing at least portions of (contents in) a data packet in the        output data or of (contents in) a data packet derived therefrom        in order to derive a second, receiver side test signal, i.e.        representing the first test signal as transmitted and as then        received at the receiver, and    -   analysing the derived second test signal by applying a        predetermined analysis criterion in order to obtain at least one        value for a quality indicator.

By combining the voice data and the test signal to form the input datain the same, first data format, there is a real intermingling of voicedata and test signal, which allows attributing a quality factor obtainedfrom the extracted second test signal to the transmitted voice data.

In a preferred embodiment, the transmittal data format is different fromthe first data format. Hence, the combining takes place prior topreparing the data for transmission. That allows attributing an effectof transmission to both of the voice data and the test signal. Forinstance, the first data format can be an analogue data format (as uponrecording of the voice data), and the transmittal data format can be adigital data format (such as for a data packet-based network).

Further preferably, therein the step of combining includes directlyproviding the input data in a second data format different from thefirst format, i.e. the combining includes performing a datatransformation. That might prove advantageous in view of a quick datahandling, if such transformation is needed anyhow. The second dataformat might directly be the transmittal data format, obtainingsynergistic effects when performing the transformation uponanalogue-to-digital conversation. Alternatively, the input data arefirst provided in the second data format and are thereafter transformedinto input data in the transmittal data format. That might help avoidingartefacts to occur.

In another preferred embodiment, the step of combining includescombining the voice data and the test data in the first data format in amanner to obtain the input data in the first data format, wherein theinput data in the first data format are thereafter transmitted in thefirst data format as the transmittal data format, or are transformedinto input data in the transmittal data format. In that embodiment, fromthe very definition of the combining in the first data formats, it isclear that the effect the transmission has on the voice data can be mosteasily be assessed by the effect on the test data. In an example, thefirst data format allows identifying amplitudes in frequency intervalsand the combining includes adding the respective amplitude in the voicedata and the amplitude in the first test signal in at least onefrequency interval. In other words, the contents in at least one minimumdata unit are combined in a manner to be changed, i.e. these content arenot preserved as such. The frequency intervals might as well be definedonly for time slots in a frequency-and-time-divided scheme, and theadding can be restricted to specific time slots defined by the firsttest signal. Moreover, the minimum data unit could be an interval intime, wherein the first test signal is inserted in a manner to besuperimposed onto the voice data, or to replace same (“beep formilliseconds”). Of course, as commonly implemented, at the receiverside, the same scheme should be used. Hence, further preferably, theoutput data as well allows to identify amplitudes in frequency intervals(for all times or specific time intervals), wherein the amplitudes inthe first test signal are predefined and wherein identical amplitudes orcorresponding amplitudes (the latter already taking into account effectsof transmission such as an amplitude reduction to be reckoned with) arealso stored in the receiver or a storage unit coupled to the receiver.Then, the step of removing includes subtracting the amplitudes stored inthe receiver or storage unit from the output data. In that manner, thevoice data can be reconstructed in an optimum manner, leading to theprevious adding of the first test data being not or hardly audible.Still further preferably, the output data are provided in the first dataformat, that enabling to reduce artefacts in the extracted voice data.In addition or alternatively, preferably, the step of analysing includescalculating at least one Pearson coefficient (or another correlationcoefficient) on the basis of individual amplitudes in the second testsignal and of corresponding individual amplitudes stored in the receiveror storage unit. As is known, correlation coefficients such as thePearson coefficient are well-suited as indicators for transmissionquality.

In a further preferred embodiment of the method, the first test signalis independent of the voice data. That allows a precise extraction ofthese at the receiver side, namely due to predefining the second testsignal corresponding to the first test signal in receivers.Alternatively, the first test signal is created in dependence of thevoice data, which would enable placing the test signal either at thosefrequencies which are of most interest to be observed with the qualityindicator. For example, in conjunction with a higher pitch voice, thefirst test signal might have higher pitch content than with a lowerpitch voice. Alternatively, it might as well be desirable to place thefirst test signal in those frequency intervals which are less occupied.For instance, the first test signal is created in a manner for the inputdata to include, due to the first test signal, enhanced amplitude valuesat those frequencies where the voice data are weak according to apredetermined criterion. The predetermined criterion might includescomparing the voice data to a reference voice spectrum (either aspredefined or as recorded with the same user responsible for the presentvoice data speaking, or as recorded with another or plural usersspeaking). Such reference voice spectrum would allow even more preciselydefining the quality indicator. Further alternatively or furtherpreferably, time stamps are associated to at least one of the voice dataand the first test signal, and these time stamps are transmitted andreceived as well and used in the step of analysing. The latter featureenables a precise association of the second test data to the first testdata.

Another preferred feature that can be implemented in addition oralternatively to features identified above to define preferredembodiments is that the voice data are continuously provided, and thatthe first test signal includes a variation over time of at least asingle spectral portion therein, allowing the first test signal to beidentified for being derived in the step of analysing. Hence, the testsignal then does not need to be predefined as to its spectraldistribution or as to individual amplitudes in frequency intervals.Rather, the receiver can most simply identify the second test signal perse, without knowing about the first test signal.

The most preferred application of the present method is in packet-basedtransmission, i.e. when the transmittal takes place by separatelytransmitting individual data packets of the input data. Here, the needfor a reliable quality indicator is rather high.

Embodiments of the inventive method of performing a telephone call caninclude acquiring voice data at a microphone and performing thepreviously defined method of determining the quality of transmittedvoice data, wherein those voice data provided in the step of providingare the acquired voice data (i.e. analogue data) or obtained on thebasis of the acquired voice data (for instance, as converted to digitaldata), and wherein during the telephone call, a reaction is provided atleast at the receiver side on the basis of at least one value of thequality indicator. Such reaction might include increasing the level ofthe volume of audio output for weak signals (usually at a low qualityindicator), or decreasing same for strong signals (usually at a highquality indicator). The reaction might as well include that a signal issent from the receiver side to another entity. A signal could be sent tothe transmitter side, such as a request to increase the amplitude levelat the transmitter side when the received signals are weak.Alternatively, the request could be for increasing the sample rate uponacquiring voice data to decrease the noise-to-signal level. The signalcould as well simply include an acknowledgement to the transmitter sidethat the quality indicator was within an interval of allowed qualityindicators. A signal could as well be transmitted to entities within thetransmission path, for instance requesting higher gain at intermediatestations if the quality indicator is beyond an interval of allowedquality indicators or in a specific interval of quality indicatorstriggering such signal to be sent.

Embodiments of a first inventive apparatus for performing a telephonecall includes a microphone for acquiring voice data and a transmittercoupled to the microphone, and further includes means to combine thevoice data with test data to form input data, said test data beingpredetermined or defined in dependence of the voice data, wherein themeans to combine provides the input data to the transmitter. Asmentioned above, the combining shall include that the data content in atleast one minimum data unit of the voice data is changed on the basis ofat least part of the test signal/test data to a different data content,namely preferably in the same at least one minimum data unit, andpreferably without changing the at least one minimum data unit as to itsdefinition and size. The minimum data unit with the method andapparatuses of the invention might be or include a frequency intervalper se or a frequency interval for a time slot. Alternatively, the testdata might be inserted into voice data in time intervals where they aresuperimposed to the voice data or where the voice date are completelyremoved.

In a preferred embodiment, the apparatus includes a clock and means toinclude (or to insert) time stamps in the input data or in data obtainedfrom the input data, such time stamps allowing to more easily recognizethe test data at the receiver side.

Embodiments of a second inventive apparatus for performing a telephonecall includes a receiver and a loudspeaker coupled to the receiver,wherein the apparatus further includes means for separating, from thefrequency spectrum of data received by the receiver, amplitude portionspertaining to test data included in the received data, and to providethe data from which the test data have been separated to theloudspeaker, and to provide the test data to an analysis unit thatanalyses the test data according to a predetermined criterion to obtaina value for a quality indicator. The advantages of such apparatus arethose of the above-described method in which the apparatus can be used.

Preferably, the means for separating includes a filter, that being mostuseful when the test data are defined with components mainly or entirelyoutside of a frequency band filtered out by the filer.

In another preferred embodiment of the second apparatus, the analysisunit comprises a transformation unit for providing a frequencytransformation of the test data, a comparing unit for comparing at leastone amplitude value in the frequency transformation to a given amplitudevalue, wherein further preferably, the at least one given amplitudevalue is stored in a storage unit of the apparatus or a storage unitcoupled thereto, and wherein still further preferably, then the at leastone given amplitude value is derived from other data transmitted.

The second apparatus might as well be having the properties of the firstapparatus and thus being usable for transmitting and receiving, as iscommon with telephone conversations.

Embodiments of the inventive system for performing a telephone callincludes at least one first apparatus as described above and at leastone second apparatus as described above, wherein a signal indicating theat least one value for a quality indicator obtained by the secondapparatus or a signal derived therefrom is transmitted from the secondapparatus to the first apparatus at least if a predeterminedtransmitting criterion is fulfilled. Hence, a kind of feedback is givento wherefrom the voice data originate.

Then, preferably, the first apparatus reacts to the signal received fromthe second apparatus in a manner to change, further preferably toimprove, the quality of the input data.

Other details, objects, and advantages of the telecommunicationsapparatus method will become apparent as the following description ofcertain exemplary embodiments thereof proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, a preferred embodiment of the invention is described withrespect to the drawing, in which:

FIG. 1 shows a system for performing a telephone call wherein theinventive apparatuses are included and the inventive methods are used,

FIG. 2 shows the receiver side apparatus of FIG. 1 in more detail forillustrating an exemplary embodiment thereof,

FIGS. 3a to 3c illustrate the superimposition of a test signal to voicedata. FIG. 3a illustrates an exemplary embodiment of a test signal atest signal as a regular sequence of plural peaks. FIG. 3b illustratesan exemplary embodiment of voice data. FIG. 3c illustrates an exemplaryembodiment of the superimposition of the test signal of FIG. 3a and thevoice data of FIG. 3 b.

DETAILED DESCRIPTION

A method of performing a telephone call between a transmitting apparatus100 and a receiving apparatus 200 includes a method of determining thequality of the transmitted voice data. The roles of the transmittingapparatus 100 and the receiving apparatus 200 can be interchanged duringthe call, in dependence of at which apparatus the user is speaking.Hence, any unit described below to be part of one of the apparatuses100, 200 can as well be part of the other apparatus 200, 100. Thetransmitting apparatus 100 and receiving apparatus 200 can each beconfigured as communication devices (e.g. terminal devices) and includea processor connected to non-transitory memory. Each apparatus caninclude input devices (e.g. microphone) and output devices (e.g.speaker) or input/output devices (e.g. touch screen display).

The apparatuses are presently connected via a packet-based data network16, i.e. the data are required to be transmitted in a digital dataformat, which means that originally acquired analogue data would need toundergo an analogue-to-digital conversion. Else, the data could directlybe acquired in the digital data format as the transmittal data format.

FIG. 1 shows that a voice input unit 10 (a microphone) acquires voicedata. A test signal generator 12 generates a test signal which ispresently independent of the voice data, i.e. includes a data schemewell-known in the overall system, for the receiving apparatus 200 torefer to such test signal. The voice data and the test signal are,according to FIG. 1, entirely added in the time domain, in adder 14.

That is depicted in more detail in FIGS. 3a to 3c , which each areshowing intensity A of volume (loudness), i.e. an amplitude, inarbitrary units over time t, the latter as well in arbitrary units. FIG.3a shows an example of a test signal as a regular sequence of pluralpeaks. FIG. 3b shows an example of voice data. FIG. 3c shows thesuperimposition of the test signal of FIG. 3a and the voice data of FIG.3b , wherein at each point in time, the intensity A of the test data hasbeen added to the intensity A of the voice data, obtaining the resultingintensity at that point in time.

The idea of the method is based on that the quality of transmission ofthe voice data of FIG. 3b can be assessed in an optimum manner byreferring to the test signal of FIG. 3 a.

Hence, after transmission over network 16, the receiving apparatus 200has to extract the test signal from the overall signal as received.First, a first filter 20 uses filter banks to remove the test signalform the overall signal, then supplies the resulting output data to aloudspeaker 22. Hence, the test signal is not or hardly audible.Simultaneously, a second filter 24 filters out the voice signal usingfilter banks, for extracting the test signal. The test signal is thenanalysed in analysing unit 26 that outputs a quality indicator, for usewithin the receiving apparatus 200 or for being sent to the transmittingapparatus 100 or to units within the network 16.

An embodiment of the analysing unit 26 is now explained in detail withrespect to FIG. 2. The analysing unit 26 includes a windowing unit 28,for being able to perform a frequency transformation, namely by limitingthe overall amount of data that are used as input for the next stage,where a frequency transformation takes place. Such windowing can beperformed by relying to detection of individual peaks. Alternatively, awindow can be defined by relying to one or more time stamps included inthe transmitted data (for which a clock would be needed withintransmitting apparatus 100 as well as in or relating to the analysingunit 26). A transformation unit 30 then provides a Fast FourierTransformation, FFT, on the basis of the limited data obtained bywindowing. A correlation calculating unit 32 thereafter calculates aPearson coefficient with respect to reference data, the latter beingstored in a storage unit (not shown) of the receiving apparatus 200, orthe latter having been acquired at an earlier time interval. Thereference data are commonly as well provided as a Fast FourierTransformation.

Following a calibration of the Pearson coefficient in calibration unit34, the result defining unit 36 defines the resulting quality indicator,and that indicator is then stored in storage unit 38, for use at a laterinstance in the course of general quality control, or for direct useduring the telephone call (requesting for causing a change intransmission quality).

Hereinbefore, the example of adding the test signal to test voice dataover the entire time has been given. However, such adding can take placein only part of the overall time, i.e. in dedicated time intervals.Moreover, the adding can as well take place in the frequency domain,such as after a frequency transformation (e.g., FFT), at the transmitterside. It also can take place within time slots in the frequency domain.The adding can take place with analogue as well with digital signals.However, it should be provided for the combining of the voice data andthe test signal to be of such kind that transmission effects act uponthe test signal included in the transmitted data in the same or at leasta similar manner than upon the voice data.

It should be appreciated that while certain exemplary embodiments of asystem, a telecommunications apparatus and methods of making and usingthe same have been shown and described above, it is to be distinctlyunderstood that the invention is not limited thereto but may beotherwise variously embodied and practiced within the scope of thefollowing claims.

The invention claimed is:
 1. A method of determining the quality oftransmitted voice data transmitted via a network for a telephone call,said method including: providing voice data at a transmitter side in afirst data format during the telephone call, providing a first testsignal in the first data format, combining the voice data and the testsignal to form input data, transmitting the input data in a transmittaldata format during the telephone call, receiving the transmitted inputdata at a receiver side to obtain output data during the telephone call,removing at least portions of a data packet in the output data or of adata packet derived therefrom by the receiver side in order to derive asecond test signal during the telephone call, analysing the derivedsecond test signal by applying a predetermined analysis criterion inorder to obtain at least one value for a quality indicator at thereceiver side during the telephone call; and in response to the receiverside determining that the at least one value for the quality indicatoris not within a pre-defined acceptable threshold during the telephonecall, the receiver side performing at least one action during thetelephone call to (i) adjust how the voice data is output at thereceiver side based on the at least one value for the quality indicatorand/or (ii) instruct the transmitter side to adjust the transmitting ofthe input data in the transmittal data format based on the at least onevalue for the quality indicator.
 2. The method of claim 1, wherein thetransmittal data format is different from the first data format.
 3. Themethod of claim 2, wherein the first data format is an analogue dataformat and the transmittal data format is a digital data format.
 4. Themethod of claim 3, wherein the combining includes directly providing theinput data in a second data format different from the first format,wherein either the second data format is the transmittal data format, orthe input data in the second data format are transformed into input datain the transmittal data format.
 5. A method of determining the qualityof transmitted voice data transmitted via a network, said methodcomprising: providing voice data at a transmitter side in a first dataformat, providing a first test signal in the first data format,combining the voice data and the test signal to form input data,transmitting the input data in a transmittal data format, receiving thetransmitted input data at a receiver side to obtain output data,removing at least portions of a data packet in the output data or of adata packet derived therefrom in order to derive a second test signal,analysing the derived second test signal by applying a predeterminedanalysis criterion in order to obtain at least one value for a qualityindicator; and wherein the combining includes: combining the voice dataand the test data in the first data format in a manner to obtain theinput data in the first data format, wherein the input data in the firstdata format are thereafter transformed into input data in thetransmittal data format, wherein the first data format allows toidentify amplitudes in frequency intervals and wherein the combiningincludes adding the respective amplitude in the voice data and theamplitude in the first test signal in at least one frequency interval,wherein the output data as well allows to identify amplitudes infrequency intervals, wherein the amplitudes in the first test signal arepredefined and wherein corresponding or identical amplitudes are alsostored in the receiver or a storage unit coupled to the receiver, andwherein the removing includes subtracting the amplitudes stored in thereceiver or storage unit from the output data, wherein a) the outputdata are provided in the first data format and/or b) the analysingincludes calculating at least one Pearson coefficient on the basis ofindividual amplitudes in the second test signal and of correspondingindividual amplitudes stored in the receiver or storage unit.
 6. Themethod of claim 5, wherein the first test signal is independent of thevoice data.
 7. A method of determining the quality of transmitted voicedata transmitted via a network, said method comprising: providing voicedata at a transmitter side in a first data format, providing a firsttest signal in the first data format, combining the voice data and thetest signal to form input data, transmitting the input data in atransmittal data format, receiving the transmitted input data at areceiver side to obtain output data, removing at least portions of adata packet in the output data or of a data packet derived therefrom inorder to derive a second test signal, analysing the derived second testsignal by applying a predetermined analysis criterion in order to obtainat least one value for a quality indicator; and wherein the first testsignal is created in dependence of the voice data and the first testsignal is created in a manner for the input data to include, due to thefirst test signal, enhanced amplitude values at those frequencies wherethe voice data are weak according to a predetermined criterion; andwherein a) applying of the predetermined criterion includes thecomparing the voice data to a reference voice spectrum, which isindividually defined for different speakers and/or b) time stamps areassociated to at least one of the voice data and the first test signal,the time stamps being transmitted and received as well and used in theanalysing.
 8. The method of claim 7, wherein the voice data arecontinuously provided, and wherein the first test signal includes avariation over time of at least a single spectral portion therein,allowing the first test signal to be identified for being derived in theanalysing.
 9. The method of claim 7, wherein the transmitting of theinput data takes place by separately transmitting individual datapackets of the input data.
 10. A method of performing a telephone call,including acquiring voice data at a microphone and performing the methodof determining the quality of transmitted voice data of claim 5, whereinthose voice data provided in the providing of the voice data are theacquired voice data or obtained on the basis of the acquired voice data,and wherein during the telephone call, a reaction is provided at leastat the receiver side on the basis of at least one value of the qualityindicator.
 11. An apparatus for performing a telephone call including: amicrophone for acquiring voice data; and a transmitter coupled to themicrophone, wherein the apparatus configured to combine the voice datawith test data to form input data, said test data being predetermined ordefined in dependence of the voice data, wherein the formed input datais formed for providing to the transmitter to form output data in atransmittal data format to transmit to a receiver side during atelephone call so at least portions of a data packet in the output dataor of a data packet derived therefrom at the receiver side is derivableto form a second test signal during the telephone call such that thederived second test signal is analysable at the receiver side viaapplication of a predetermined analysis criterion in order to obtain atleast one value for a quality indicator at the receiver side during thetelephone call and, in response to the receiver side determining thatthe at least one value for the quality indicator is not within apre-defined acceptable threshold during the telephone call, at least oneaction during the telephone call is performable by the receiver side to(i) adjust how the voice data is output at the receiver side based onthe at least one value for the quality indicator and/or (ii) instructthe apparatus to adjust the transmitting of the input data in thetransmittal data format based on the at least one value for the qualityindicator; the apparatus also configured to respond to at least oneinstruction received from the receiver side to adjust transmitting ofthe input data in the transmittal data format that is based on the atleast one value for the quality indicator during the telephone call. 12.The apparatus of claim 11, further including a clock, the apparatusconfigured to include time stamps in the input data or in data obtainedfrom the input data.
 13. An apparatus for performing a telephone callincluding: a receiver and a loudspeaker coupled to the receiver, whereinthe apparatus is configured to separate, from a frequency spectrum ofdata received by the receiver during a telephone call from a transmitterside, amplitude portions pertaining to test data included in thereceived data and to provide the data from which the test data have beenseparated to the loudspeaker, and to provide the test data to analysethe test data according to a predetermined criterion to obtain a valuefor a quality indicator and, in response to determining that the atleast one value for the quality indicator is not within a pre-definedacceptable threshold during the telephone call, perform at least oneaction during the telephone to (i) adjust how voice data is output atthe loudspeaker based on the at least one value for the qualityindicator and/or (ii) instruct the transmitter side to adjusttransmission of the data being received at the receiver based on the atleast one value for the quality indicator.
 14. The apparatus of claim13, wherein: a) apparatus includes at least one filter; and/or b) theapparatus is configured to provide a frequency transformation of thetest data, compare at least one amplitude value in the frequencytransformation to a given amplitude value, the at least one givenamplitude value being storeable in a storage unit of the apparatus or astorage unit coupled thereto.
 15. The apparatus of claim 14, wherein atleast one given amplitude value is derived from other data transmittedto the apparatus.
 16. The apparatus of claim 13, comprising: amicrophone for acquiring voice data; and a transmitter coupled to themicrophone, the apparatus also configured to combine the voice data withtest data to form input data to provide the input data to thetransmitter, said test data being predetermined or defined in dependenceof the voice data.
 17. The apparatus of claim 16, further including aclock for generating time stamps, the apparatus configured to includethe time stamps in the input data or in data obtained from the inputdata.
 18. A system for performing a telephone call comprising: at leastone first apparatus, the first apparatus being an apparatus of claim 11;and at least one second apparatus, the second apparatus including: areceiver and a loudspeaker coupled to the receiver, wherein the secondapparatus is configured to separate, from a frequency spectrum of datareceived by the receiver during a telephone call, amplitude portionspertaining to test data included in the received data and to provide thedata from which the test data have been separated to the loudspeaker,and to provide the test data to analyse the test data according to apredetermined criterion to obtain a value for a quality indicator and,in response to determining that the at least one value for the qualityindicator is not within a pre-defined acceptable threshold during thetelephone call, perform at least one action during the telephone to (i)adjust how voice data is output at the loudspeaker based on the at leastone value for the quality indicator and/or (ii) instruct the firstapparatus to adjust transmission of the data being received at thereceiver based on the at least one value for the quality indicator; andthe first apparatus configured to respond to instruction from the secondapparatus to improve quality of the data being transmitted to thereceiver during the telephone call.